REGULATION OF THE TRANSPOSABLE ELEMENT MARINER

The mariner/Tc1 superfamily of transposable elements is widely distrib uted in animal genomes and is especially prevalent in insects. Their w ide distribution results from their ability to be disseminated among h osts by horizontal transmission and also by their ability to persist i n genomes through multiple speciation events. Although a great deal is known about the molecular mechanisms of transposition and excision, v ery little is known about the mechanisms by which transposition is con trolled within genomes. The issue of mariner/Tc1 regulation is critica l in view of the great interest in these elements as vectors for germl ine transformation of insect pests and vectors of human disease. Sever al potentially important regulatory mechanisms have been identified in studies of genetically engineered mariner elements. One mechanism is overproduction inhibition, in which excessive wild-type transposase re duces the rate of excision of a target element. A second mechanism is mediated by certain mutant transposase proteins, which antagonize the activity of the wild-type transposase. The latter process may help exp lain why the vast majority of MLEs in nature undergo 'vertical inactiv ation' by multiple mutations and, eventually, stochastic loss. Another potential mechanism of regulation may result from transposase titrati on by defective elements that retain their DNA binding sites and abili ty to transpose. There is also evidence that some mariner/Tc1 elements can be mobilized in a type of hybrid dysgenesis.